1. Field of the Invention
The present invention relates to a microcomputer and its access speed control method, which is useful when applied to a microcomputer used in electronic equipment of various instruments disposed in a high dose radiation-exposed environment.
2. Description of the Related Art
In a high dose radiation-exposed environment, electronic parts of electronic equipment deteriorate under the influence of radiation. Since function and performance of the electronic parts decline, their long-term use has been impossible.
A conventional microcomputer, in particular, has its semiconductor parts (IC, LSI) rapidly deteriorated by radiation, resulting in marked changes in the characteristics of the semiconductor parts. Consequently, decline in the function and performance of the microcomputer, and its operating defects may occur. Thus, the conventional microcomputer cannot be used for a long period (2 years or more) in a high dose radiation-exposed environment, and had to be used in a radiation-free environment. FIG. 5 is an explanation drawing showing an example of use of a conventional microcomputer.
As shown in this drawing, only a working instrument 32 is installed in a high dose radiation-exposed environment (area A in the drawing) surrounded by a shielding member 33. A microcomputer 31 for controlling this working instrument 32 is installed in a radiation-free environment outside the shielding member 33 (area B in the drawing). To transmit electrical signals between the working instrument 32 in the radiation-exposed environment and the microcomputer 31 in the radiation-free environment, many (e.g., 200 to 300) electrical signal cables 34, over a long distance (e.g., about 100 m), are wired from the working instrument 32 to the microcomputer 31.
As described above, the conventional microcomputer 31 cannot be used in a radiation-exposed environment. Therefore, the working instrument 32, in a radiation-exposed environment, and the microcomputer 31, in an environment not exposed to radiation, must be electrically connected together by the electrical signal cables 34. This has posed the following problems:
1 An increase in the number of the electrical signal cables 34 in the radiation-exposed environment has necessitated a large radiation-exposed environment area (such as cells of nuclear power related facilities), induced cost buildup, and made maintainability poor. PA0 2 Since the electrical signal cables 34 in the radiation-exposed environment becomes longer, weak signals such as sensor signals cannot be transmitted, or transmission accuracy decreases. PA0 3 The microcomputer 31 cannot be carried on a mobile member in the radiation-exposed environment. Hence, neither a complicated task nor a high precision task can be accomplished by using the mobile member, thus making it difficult to mechanize operations in the radiation-exposed environment.